The mosquite-borne nematode parasite Brugia malayi and other related filarial nematodes cause chronic infections (filariasis) in one-third to one-half billion people living in the tropics. In advanced cases these infections can lead to elephantiasis. Since detection and identification of different species of Brugia are extremely difficult, repeat DNA sequences are cloned for possible use as genus or species-specific probes. Hha I, Alu I or Rsa I restriction endonuclease digests of B. malayi DNA demonstrate the existence of a family of highly repeated sequences 320 base pairs in length (the Hha I repeat DNA family). A 640 base pair dimer of this repeated sequence is cloned in the plasmid pBR322. Using dot hybridization, this repeat family is found to make up about 12% of the B. malayi genome. Restriction site mapping and DNA sequence analysis show that members of this repeat family are arranged in tandem, direct arrays. Brugia pahangi, a closely related animal parasite, has a related repeat DNA sequence which cross hybridizes with the cloned B. malayi repeat. Cleavage of B. pahangi DNA with Hha I (but not Alu I or Rsa I) demonstrates that this sequence is also approximately 320 base pairs long and organized in direct, tandem arrays. At least ten copies of the Hha I repeat will be cloned and sequenced from both B. malayi and B. pahangi. Sequence heterogeneity will be compared both within and between species. The structure of the individual repeats, the organization of the repeat clusters, and the location of the repeat clusters on chromosomes will be investigated. Since this repeat DNA family makes up only a portion of the total repeat DNA found in Brugia, we will clone and sequence members of other repeat DNA families. Cloned repeat DNA sequences will be evaluated as species-specific hybridization probes. Finally, we intend to extend this analysis of repeat DNA to other species of Brugia, and possibly other parasites.